1. Field of the Invention
The present invention relates to a pulse tube refrigerator, and more particularly, to a pulse tube refrigerator, which is capable of increasing the available area of a cold heat exchanger and of reducing the size of a refrigerator.
2. Description of the Background Art
In general, a cryogenic refrigerator is a refrigerator of low oscillation and high reliability, which is used for refrigerating small electronic parts or a superconductor. A stirling refrigerator, a Giford-Mcmahon (GM) refrigerator, and a Joule-Thomson refrigerator are widely known.
However, the reliability of such refrigerators deteriorates when the refrigerators are driven at high speed. Also, additional lubricating means must be included for the abrasion of the portions that undergo friction during the driving of the refrigerators. Therefore, a cryogenic refrigerator, whose reliability is maintained during the high speed driving and which needs not be repaired for a long time because additional lubrication is not necessary, has been recently required. One of such cryogenic refrigerators is a pulse tube refrigerator.
FIG. 1 is a schematic sectional view showing an example of a conventional pulse tube refrigerator. As shown in FIG. 1, the conventional pulse tube refrigerator includes a driving unit 10 for generating the reciprocal movement of a working gas and a refrigerating unit 20 having a cold head due to the thermodynamic cycle of the working gas that is sucked up into/discharged from the driving unit 10 and is in a reciprocal movement in a plumbing line.
The driving unit 10 includes a closed case 11 having an inner space that shields a middle housing 11b and a lower housing 11c, an upper housing 11a, which is tightly coupled to the upper peripheral edge of the closed case 11 and in the middle of which a cylinder 10a is formed, a piston 14, which is located in the closed case 11, whose upper surface is tightly-coupled to the bottom of the upper housing 11a, to the inside of which an elastic supporter 15 is fastened, and which is inserted into the cylinder 10a, the middle housing 11b, in which a driving motor 12 including a driving axis 13 connected to the piston 14 is fixedly loaded, the lower housing 11c, which is located in the closed case 11, whose upper surface is tightly coupled to the lower surface of the middle housing, and to the inside of which an elastic supporter 16 is fastened, and a cover 11d, whose upper surface is tightly coupled to the bottom of the lower housing 11c. 
The refrigerating unit 20 includes an aftercooler 21, which is tightly coupled to the upper housing 11a of the driving unit 10 and is connected to the cylinder 10a, a regenerator 22 connected to the other end of the aftercooler 21, a cold heat exchanger 23A connected to the other end of the regenerator 22, a pulse tube 23 connected to the other end of the cold heat exchanger 23A (that is, the inlet of the pulse tube), a hot heat exchanger 23B connected to the other end of the pulse tube 23 (that is, the outlet of the pulse tube), an inertance tube 24 connected to the other end of the hot heat exchanger 23B, a reservoir 25 connected to the other end of the inertance tube 24, and a sealed cell 26, which holds the regenerator 22 and the pulse tube 23, whose lower surface is tightly coupled to the upper surface of the aftercooler 21, in the middle portion of whose upper surface a through hole corresponding to the outer circumference of the pulse tube 23 is formed, and the middle portion of whose upper surface is tightly coupled to the outer circumference of the pulse tube 23.
The aftercooler 21 is formed of a metal and performs a function of a heat exchanger for removing the heat generated in the working gas when the driving unit 10 compresses the working gas.
The regenerator 22 is a kind of a heat exchanger for providing a means for letting the maximum amount of potential work (cooling power) reach a low temperature region with the working gas not having much heat. The regenerator 22 does not simply provide heat to a system or remove heat from the system.
The regenerator 22 absorbs heat from the working gas in a part of a pressure cycle and returns the absorbed heat to the pressure cycle in another part.
The cold heat exchanger 23A absorbs heat from a member to be cooled and forms the cold head.
The pulse tube 23 moves heat from the cold heat exchanger 23A to the hot heat exchanger 23B when a suitable phase relationship is established between a pressure pulse and the mass flow of the working gas in the pulse tube 23.
The hot heat exchanger 23B removes the heat that passed through the pulse tube 23 from the cold heat exchanger 23A.
The inertance tube 24 and the reservoir 25 provide a phase shift so that heat flow can be maximized under an appropriate design.
The conventional pulse tube refrigerator operates as follows.
When power is applied to the driving motor 12, the driving axis 13 is in a linear reciprocal movement together with the elastic supporters 15 and 16. The piston 14 integrally combined with the driving axis 13 is in the linear reciprocal movement in the cylinder 10a and sucks up/discharges the working gas of the refrigerating unit 20, to thus form the cold head in the cold heat exchanger 23A.
That is, the working gas compressed in the cylinder 10a and pushed out of the cylinder 10a when the piston 14 compresses the working gas is refrigerated to an appropriate temperature through the aftercooler 21 and is flown to the regenerator 22. The working gas that passed through the regenerator 22 is flown to the cold heat exchanger 23A of the pulse tube 23 and pushes the working gas filled in the pulse tube 23 toward the hot heat exchanger 23B. The working gas emits heat, while passing through the hot heat exchanger 23B, and is flown to the reservoir 25 through the inertance tube 24.
At this time, because the mass flow of the working gas that flows through the inertance tube 24 is relatively smaller than the mass flow of the working gas flown to the pulse tube 23, the inside of the pulse tube 23 forms thermal equilibrium at a high pressure.
When the working gas flown to the pulse tube 23 during the suction of the working gas by the piston 14 is returned to the cylinder 10a, while passing through the regenerator 22, the mass flow of the working gas returned to the pulse tube 23 through the inertance tube 24 is relatively smaller than the mass flow of the working gas returned from the pulse tube 23. Therefore, the working gas in the pulse tube 23 adiabatic expands. In general, the working gas rapidly adiabatic expands in the cold heat exchanger 23A. Therefore, the cold head is formed in the cold heat exchanger 23A.
Therefore, the inside of the pulse tube 23 forms the thermal equilibrium at a low pressure. The working gas continuously moves from the reservoir 25 to the pulse tube 23 through the inertance tube 24 and increases the pressure of the working gas in the pulse tube 23, to thus recover the initial temperature. Such a series of processes are repeated.
However, in the refrigerating unit of the conventional pulse tube refrigerator, the area of the cold heat exchanger 23A, to which a member to be actually refrigerated is attached, is narrow. Therefore, there is a limitation in refrigerating a large amount of members.
That is, the regenerator 22 is combined with one side of the cold heat exchanger 23A and the pulse tube is combined with the other side of the cold heat exchanger 23A. Therefore, the available area, to which the members to be refrigerated can be attached, is restricted to the outer circumference of the cold heat exchanger 23A.
As shown in FIG. 1, the entire length of the refrigerator increases because the regenerator 22, the pulse tube 23, the inertance tube 24, and the reservoir 25 are installed in a line. Therefore, a larger installment space is required.
Also, although the regenerator 22 and the pulse tube 23 must be vacuum insulated from each other and the hot heat exchanger 23B, the inertance tube 24, and the reservoir 25 must be exposed to the outside, the above-mentioned members are installed in a line. Accordingly, at least two sealing portions and members are required in order to combine the sealed cell 26 with the pulse tube 23. Therefore, the number of parts becomes excessive.
Therefore, an object of the present invention is to provide a pulse tube refrigerator, which is capable of increasing the available area of a cold heat exchanger having a uniform area.
Another object of the present invention is to provide a pulse tube refrigerator, which is capable of reducing a restriction on an installing space by reducing the length of a refrigerating unit.
Still another object of the present invention is to provide a pulse tube refrigerator, which is capable of reducing production cost by reducing the number of sealing members for vacuum insulating the refrigerating unit.
To achieve these and other advantages and in accordance with the purposes of the present invention, as embodied and broadly described herein, there is provided a pulse tube refrigerator, comprising an aftercooler connected to a cylinder for sucking up/discharging a working gas, the aftercooler for removing the heat caused by the compression of the working gas sucked up into/discharged from the cylinder, a regenerator connected to the aftercooler, the regenerator for storing the sensible heat of the working gas passing through the regenerator and returning the sensible heat when the working gas inversely passes through the regenerator, a pulse tube connected to one end of the regenerator, the pulse tube for compressing/expanding the working gas passing through the regenerator and forming heat flow, an inertance tube and a reservoir connected to the pulse tube, the intertance tube and the reservoir for causing phase shift between a pressure pulse and mass flow and generating the heat flow in the pulse tube, a hot heat exchanger for connecting the pulse tube to the inertance tube and for emitting the moved heat, and a cold heat exchanger for covering the regenerator and the pulse tube together such that connection channels are formed inside the cold heat exchanger in order to connect the regenerator to one end of the pulse tube inserted into the regenerator. The cold heat exchanger comprises a hollow cylindrical body combined with the outer circumference of the regenerator, a roughly hollow cylindrical central body, having a step and contacting and combined with the leading end of the pulse tube located in the middle of the body and the inner circumference of the regenerator, and a cover inserted into and combined with the inner circumference of the body on the body.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.